Pressurized hydraulic fluid in a transmission line pressure circuit actuates clutches in vehicles with automatic transmission systems. Sufficient line pressure must be applied in the automatic transmission systems with variable line pressure control to prevent applied clutches from slipping. However, it is also preferable to minimize line pressure to conserve fuel. An unnecessarily high line pressure may also cause a line pressure regulating system to enter a priority mode, which restricts oil flow to a transmission oil cooler.
An ideal line pressure is determined based on input torque to the transmission. However, torque increases when the vehicle accelerates and during other transient maneuvers. Proper line pressure must be applied simultaneously with the increase in torque. Because of hydraulic delays in a transmission line pressure control system, the input torque to the transmission is estimated prior to an actual increase in torque in the transmission so that a proper line pressure can be applied by the time the increase in torque takes place.
Some automatic transmissions include an electronically controlled capacity clutch (ECCC). An ECCC must apply proper pressure concurrently with the increase in input torque to prevent excessive torque flares and closed loop controller wind up. The input torque is estimated prior to the actual increase in torque to ensure that the clutch carries sufficient feed forward slip control.
In one conventional approach, the input torque to the transmission is estimated based on measured mass airflow in an intake manifold of the engine. However, mass airflow-based torque estimation is not accurate during transient maneuvers and does not significantly lead actual torque. In another conventional approach, the input torque is estimated based on a position of a throttle in the vehicle. However, throttle-based torque estimation is not as accurate as mass airflow-based torque estimation during steady-state conditions.
Conventional automatic transmission systems estimate torque in a worst case scenario, which leads to excessive line pressure application and ECCC instability.